1. Field of the Invention
The present invention generally relates to aircraft wing assemblies. More particularly, the invention relates to a wing assembly for an aircraft moveable slat system having a contoured surface to improve airflow.
2. Technical Background
It is well documented that improving aerodynamics is a central goal of the aircraft manufacturing industry. Due to cost and safety concerns, certain wing assemblies have particularly been the focus of attention moreso than others. For example, the leading edge of a typical aircraft wing will have an inboard slat as well as a number of outboard slats. Leading edge slats are critical to the improvement of the takeoff and landing performance of the aircraft. For example, when the slats extend, they increase the aerodynamic lift of the wing. The leading edge slats also function to increase the angle of attack at which the wing stalls. Thus, a typical moveable slat system for an aircraft wing will include a slat having an outer geometry which defines a leading edge of the aircraft wing, and an actuation mechanism. The actuation mechanism is coupled to the slat for positioning the slat with respect to the aircraft. The moveable slat system will also have a wing assembly (or Surface-1) positioned immediately adjacent to the slat such the actuation mechanism extends through a cutout of the wing assembly. As will be discussed below, this cutout can be particularly troublesome with regard to aerodynamic lift.
The region between the slat trailing edge and the edge structure is typically gapped for landing configurations. This provides the largest amount of aerodynamic lift for a given wing area. This gapped region experiences high velocity aerodynamic flows especially during maximum lift conditions. The above-discussed cutout is located in a region of the wing where disruptions in the flow field can affect the maximum lift generated by the entire wing. The amount of exposed cutout above the slat trailing edge at landing has therefore been correlated with increased aerodynamic losses.
One technique to minimize the cutout penalty is referred to as the dual pivot design. The dual pivot design uses a slat position for landing which completely covers the cutout. This approach has been used on various wing designs, and requires an auxiliary track system to obtain the high slat height. The auxiliary track system, however, comes at a significant cost. Cost figures have been on the order of $250,000 per aircraft relative to a single pivot slat system (to be described below). It is therefore desirable to provide a moveable slat system that does not require an auxiliary track system in order to minimize the aerodynamic losses associated with the wing assembly cutout.
The single pivot slat design was developed to provide equivalent aerodynamic performance as the dual pivot design but without the need for an auxiliary track system. The single pivot design has a lower slat trailing edge height at landing relative to a dual pivot slat system. The lower height exposes a larger amount of cutout to the high velocity air stream which exists above the slat trailing edge on the wing top surface. The cutout problem is addressed in this approach with a fully articulating track door system to cover the cutout. There are a number of difficulties, however, associated with the track door system. For example, the doors are expensive due to part count and complexity. Costs on the order of $50,000 per aircraft have been experienced. Furthermore, the doors require a fairly large actuating spring to allow closure. This increases forces to the door, thereby requiring a heavier structure. In addition, the doors slide in tracks with fairly small slots between the door and the track. The slot could be prone to blockage due to heavy icing conditions, especially in the case of glare ice.
Furthermore, it is important to note that moving devices generally require more maintenance than fixed devices. The above-described track door system also has a number of failure modes such as freezing in the up position, or freezing in the down position. When the door system freezes in the down position, retraction can result in breakage. It is also known that both of these failure modes leave the cutout unprotected with a subsequent loss in aerodynamic performance. It is therefore desirable to provide a wing assembly for an aircraft wing moveable slat system that does not have moveable hardware. The elimination of moveable hardware would provide a number of unique benefits. For example, the resulting system would be cheaper and more simply manufactured. Furthermore, eliminating the need for actuation improves reliability and setup time.
The above and other objectives are provided by a wing assembly for an aircraft moveable slat system in accordance with the present invention. The wing assembly has a fixed structure and a contoured surface. The fixed structure has an exterior surface defining an external contour and an interior surface defining a cavity. The fixed structure also has one or more edges defining a cutout. The contoured surface is coupled to one or more of the edges of the cutout and extends into the cavity. The contoured surface promotes airflow from the cavity to the external contour. The result is a solution to aerodynamic losses that does not require an auxiliary track system or moving parts.
Further in accordance the present invention, a moveable slat system for an aircraft wing has a slat, an actuation mechanism, and a wing assembly. The slat has an outer geometry which defines a leading edge of the aircraft wing. The actuation mechanism is coupled to the slat for positioning the slat with respect to the aircraft. The wing assembly is positioned adjacent to the slat such that the actuation mechanism extends through a tailored cutout of the wing assembly. Providing a tailored cutout in a moveable slat system represents an improvement over conventional systems with respect to costs, aerodynamic lift, and weight.
Further in accordance with the present invention, a method for directing airflow from a wing assembly cavity of an aircraft wing to a top surface of the wing is provided. The method includes the steps of defining the cavity and an external contour with a fixed structure, and defining a cutout with one or more edges of the fixed structure. A contoured surface is then coupled to one or more of the edges of the cutout such that the contoured surface extends into the cavity and promotes airflow from the cavity to the external contour.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute part of this specification. The drawings illustrate various features and embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.